The total synthesis of cholecystokinin-pancreozymin is carried out in order to establish the correctness of the amino acid sequence determined by degradation. Analogs of secretin are prepared with the objective of finding relationships between the structure of the hormone and its biological activities. Improvements are sought in the methodology of peptide synthesis in solution and on polymeric supports. BIBLIOGRAPHIC REFERENCES: M. Bodanszky, M.L. Fink, Y.S. Klausner, S. Natarajan, K. Tatemoto, A.E. Yiotakis and A. Bodanszky, Side Reactions in Peptide Synthesis IV. Extensive O-Acylation in Histidine Containing Peptides, J. Org. Chem. 42, 00 (1977), in press. Y.S. Klausner and M Bodanxky, Cholecystokinin - Pancreozymin. II. Synthesis of a Protected Heptapeptide Hydrazide Corresponding to Sequence 17-23, J. Org. Chem. 42, 000 (1977), in press.